The invention relates generally to optical communication systems and, more specifically, to optical collimators used in optical communication systems.
Optical communication systems use collimating lenses to transfer light from optical waveguides or fibers to other optical elements. Typically, light exiting an optical fiber will rapidly diverge. In order to efficiently transmit the optical signal, it is desirable to capture as much of the diverging light as possible. Collimating the exiting light beam is one method to accomplish this. Collimating the light beam involves positioning a collimating lens to receive the optical signal in such a way that substantially parallel light exits the collimating lens. Ideally the end of the fiber should be cut at right angles to its axis so that the light exiting the fiber will be parallel to its axis. However, one major difficulty with this technique is that portions of the optical signal will be reflected by the end surface of the cut fiber and propagated in a reverse direction through the optical fiber. This is an undesirable condition known as back reflection. One way to minimize back reflections is to cut the end of the optical fiber at an angle so that reflected light is not guided in the fiber. In this way, much of the reflected light will be lost and not returned through the optical fiber.
One way to minimize back reflection is shown in FIG. 1, where the end of an optical fiber 10 contained within ferrule 20 is polished at the standard Angular Physical Contact (APC) angle of 8xc2x0. As a result, a principle light beam coming out of the end of the fiber deviates from the fiber axis. The resultant angle of the light beam exiting the fiber can be shown, using Snell""s law, to be approximately 3.62xc2x0 (shown as angle 26) for a typical communication fiber. To properly align fiber 10 to a collimating lens 12, a ferrule 20 containing the fiber 10 is inserted into a collimator housing 22 and the angle 26 of the ferrule 20 to the axis 24 should be 3.62xc2x0 to ensure that the light exiting the fiber along the axis 24 is coincident with the axis 13 of the collimating lens 12.
Although the axis of the fiber 10 is aligned to the axis of the ferrule 20, it is difficult to reliably and consistently align the ferrule 20 to the housing 22 at the correct angle and in the correct location. Any misalignment will result in degraded collimation. In the event that the end of the fiber 10 is misaligned, for example if it is located at point 25 instead of point 23, or if its actual angle 26 does not accurately compensate for the angle of the light beam exiting the fiber 10, the light exiting collimator lens 12 will deviate from the desired axis 24. In order to construct a transverse spatial mode transformer, such as the one described in pending U.S. patent applications Ser. No. 09/249,830, 09/248,969 and 09/249,920 all filed on Feb. 12, 1999 whose contents are incorporated by reference and which are assigned to the assignee of this application, the collimation must be sufficiently accurate. Prior art methods generally are either cost prohibitive or not accurate enough to be used in precision applications.
The present invention relates to a multi-element assembly and a method for aligning a first component and a second component inside the assembly. The multi-element assembly includes an object having spherical surface, a first component, and a second component. The object includes a first bore and a second bore. The first and second bores have longitudinal axes which intersect at a predetermined angle. In one embodiment the object has a center and the longitudinal axes of the first and second bores intersect the center. In another embodiment the first component is an optical fiber. In another embodiment the second component is a lens. In a further embodiment, the lens is a collimating lens.
The method includes the steps of providing an object having a spherical surface and generating a first bore and a second bore in the object. The first and second bores have longitudinal axes which intersect at a predetermined angle. The method also includes the steps of positioning a first component in the first bore at a first position and positioning a second component in the second bore at a second position. In one embodiment the first and second components are separated by a predetermined distance.